Thermal protection systems (TPS) used in connection with spacecraft, atmospheric entry vehicles, hypersonic vehicles and the like typically consist of an outer layer of ablative insulating material formed over a metallic or composite substrate. By gradually ablating or changing phase under extreme thermal exposure, the ablative layer protects the spacecraft from the intense heat produced by friction as it moves through a gaseous atmosphere. As ablation involves phase change of a material followed by exfoliation or physical transport and recession of a charred surface layer of TPS material, it is desirable to monitor the rate of recession and the thermal performance of the TPS material (e.g., during re-entry). This is particularly the case during initial entries of a new spacecraft heat shield where it is desirable to validate actual flight environments and thermal performance to predicted performance based on ground-based testing and analysis.
Known methods of sensing the state of TPS systems include the use of numerous sensors embedded in the TPS and remote electronic circuits that interface with the sensors, read the signals, convert the signals to digital data, and transmit the signals to a flight computer or data recording device. Such circuits may include voltage amplifiers, multiplexers, analog-to-digital converters, pressure-to-electrical transducers, and serial digital transmission circuits. The ambient temperature range for such devices is limited to the operating specifications of the electronics—typically −55° C. to 125° C. The ambient temperature on the backside of the TPS can reach as high as 260° C. Therefore, the electronic circuits that perform the interface to the TPS sensors are typically located away from the TPS shield or enclosed in protective box for thermal conditioning. Such boxes add substantial mass, complexity and cost to the TPS system.
Furthermore, when the interfacial electronic circuits are located away from the TPS layer, longer wires are required to connect the TPS sensors to the system. Heavier gauge connecting wires are typically used because they exhibit lower resistivity and minimize errors resulting from the resulting voltage drop, but are heavier and thus increase overall sensor system mass.
Accordingly, it is desirable to provide compact and light-weight systems for sensing the state of a TPS layer and its operating environment. Furthermore, other desirable features and characteristics of the various embodiments will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.